As your lenders what their max credit is to anyone borrower, if your dealing with a smaller community bank they will have a loan limit per borrower..

So, after this the new buyer went to the bank, borrowed 100% of the cost of property he paid, and the prior owner/tenant, is paying more for rent than what the mortgage is on the property.  

Does it become continually easier to borrow money or harder as I take on more loans?  

It could be borrow at 5% to make 10%, higher, lower, etc, etc.Its all about managing your cash flows minimize the downside and maximize the upside.

In my personal investing, I am not a fan of debt BUT I do borrow some to help achieve certain goals.

So when you receive a payoff from the borrower, amounts above your cost basis is a gain.  

How should I analyze the borrower as a flipper?

That income will be aggregated with all other income, properly accounted for and used to offset the Borrower's liabilities.  

Take the gross income, x .43 then subtract reported monthly bills such as car, credit cards student loans child support etc. whatever is left is what the seller, or borrower, can qualify for. in other words...have them complete a 1003 with a lender to see. 

A partner and I will be borrowing money for a unknown rehab project.